The present invention relates to subterranean treatments and, more particularly, in one or more embodiments, to introducing a relative permeability modifier into a subterranean interval ahead of, or in conjunction with, a chelating agent.
Chelating agents may be useful in a variety of subterranean operations including, but not limited to, chemical stimulation operations, damage removal operations, scale removal operations, filter cake removal operations, and acid-soluble cement removal operations. Chelating agents may be used to prevent precipitation of various compounds, which may be dissolved in the treatment fluid, by keeping ions in a soluble form until the treatment fluid can be returned to the surface. Chelating agents may also be useful for removal operations in acid sensitive formations.
When using chelating agents, it is often desired to treat an interval of a subterranean formation having sections of varying permeability. Consequently it may be difficult to obtain a uniform distribution of the chelating agent through the entire interval. For instance, the chelating agent may preferentially enter portions of a subterranean formation with high permeability at the expense of portions of the subterranean formation with lesser permeability. In some instances, these intervals with variable permeability may be water-producing intervals.
In an attempt to facilitate the uniform distribution of chelating agents throughout an entire interval, a variety of techniques have been used to divert the chelating agents to less permeable portions of a subterranean formation. Such techniques have involved, among other things, the injection of particulates, foams, or blocking polymers (e.g., crosslinked aqueous gels) into the subterranean formation so as to plug off the high-permeability portions of the subterranean formation, thereby diverting subsequently injected fluids to less permeable portions of the subterranean formation. While each of these diversion techniques has been used successfully, there may be disadvantages. In some instances, plugging off the high-permeability sections may not be suitable for a producing formation, for example, because the injected solution (or material) may reduce or stop the flow of hydrocarbons in addition to the achieving a desired diversion of the treatment fluid. Therefore, to return the formation to production, expensive and/or time-consuming remedial treatments may be required to remove the injected solution (or material). Furthermore, techniques geared toward injecting solutions (or materials) designed to plug off high-permeability portions of the subterranean formation may require expensive zonal isolation, which may be inaccurate, leading to inadvertent plugging of and/or damage to the hydrocarbon-bearing sections.